crimson/os/seastore: construct TransactionManager classes after device mount

crimson/os/seastore: construct TransactionManager classes after device mount

To construct TransactionManager after all the devices are discoverred.

Also, it makes the following cleanups possible:
* Cleanup SeaStore and TransactionManager factory methods.
* Decouple TransactionManager from SegmentManagerGroup.
* Drop the unnecessary tm_make_config_t.
* Drop the unnecessary add_device() methods.

Signed-off-by: Yingxin Cheng <yingxin.cheng@intel.com>